1. Field of the Invention
Bi-directional optical communications of arbitrary signals, including but not limited to digital communication streams or short pulses (for example), at the same or differing wavelengths, either coupled to optical fibers or propagated in free space, whereby an interference filter is disposed on or in the photodetector.
2. Description of Related Art
Optical wavelength division multiplexing is a known technique for combining a plurality of optical signals having different wavelengths and inserting the wavelengths into a single optical fiber. The multiple wavelength signal is transmitted through the fiber to a receiving end where the wavelengths are separated and de-multiplexed accordingly. Typically, the wavelengths are multiplexed and de-multiplexed by the use of diffraction gratings or thin film interference filters. These devices provide a spectral selectivity that is predetermined in accordance with the wavelengths in use.
A known bi-directional optical transmission and reception arrangement has an optical transmitter, which is a laser diode, and an optical receiver, which is a photodetector with an absorbing region. Such an optical delivery arrangement comprises two optical lenses. One of the lenses is for optically imaging a laser beam of the first wavelength emitting from the laser diode on a specific spatial point at a distance from the laser coincident with the end of a fiber, and the other lens is for the optical imaging of the second wavelength emitting from the fiber end onto a photodetector. The arrangement includes optical shielding means which is composed of a separate, wavelength-selective optical filter arranged obliquely in the beam path of the radiation of the two wavelengths, and this optical filter is non-transmissive for one of the two wavelengths and is only transmissive for the other of the two wavelengths.
One advantage that results from the use of wavelength division multiplexing is that a single optical fiber can simultaneously carry a plurality of data signals, sometimes in two directions.
The conventional bi-directional transmission and reception systems suffer from numerous drawbacks related to the size and separate packaging of the individual devices, the cost of manufacture, as well as the difficulty associated with alignment of the system.
The need therefore exists for a compact bi-directional transmission/reception system having a compact and economical design and layout.